By The Zagosa Team. Published .
Reviewed or updated .
Balancing water is a chain of linked steps. Sort the early links and the later ones tend to line up on their own. Get the order wrong and you can spend days chasing a reading that would have settled by itself. The sequence that works is alkalinity, then pH, then calcium, then sanitiser.
Alkalinity leads, pH follows
Total alkalinity is the buffer that keeps pH steady. If alkalinity is wrong, pH simply will not stay where you set it.
Bring alkalinity into the 80 to 120 ppm band before you touch pH. Add alkalinity increaser slowly, leaving an hour between doses and retesting each time.
With alkalinity sitting in band, pH usually drops into 7.4 to 7.8 by itself. If it does not, a small pH tweak at this point is both meaningful and lasting.
Calcium comes third
Once alkalinity and pH are steady, test calcium hardness, aiming for 100 to 250 ppm in a hot tub.
Too little calcium brings foaming, etched grout on nearby tiles and copper pickup from heater elements. Too much brings scale on the heater and along the waterline.
In hard-water parts of the UK calcium is rarely too low. In soft-water postcodes, such as parts of Scotland, the North West and South West Wales, calcium hardness increaser is essential and often forgotten.
Sanitiser goes last
With alkalinity, pH and calcium all right, your sanitiser holds its level and works efficiently. Chlorine or bromine added before the chemistry is sorted is largely wasted.
Dose to the bathing band, 3 to 5 ppm for chlorine or 4 to 6 ppm for bromine, wait an hour and retest. Adjust if you need to.
Finally, check combined chlorine. Anything above 0.5 ppm calls for a non-chlorine oxidiser shock, which works far better now the chemistry is right than it would have done earlier.
FAQ
What if everything is out at once?
This is common after a long gap in use. Fix each reading one at a time in order, with an hour between them, and resist dosing the lot in one go. The full sequence is a Saturday morning of work and leaves you with a tub that stays stable for weeks.
Can I leave alkalinity if it is only just off?
If it is within 10 ppm of band, yes. If it is 30 ppm out, no. Every step that follows depends on alkalinity being right.